It is known to manufacture automotive instrument panels containing airbag doors which are concealed from the view of a vehicle occupant prior to deployment. Such concealed airbag doors are often characterized by the non-existence of any definitive seam, styling line, gap, or similar feature between the airbag door and instrument panel outer surfaces which would indicate the airbag door's presence. An example of such a structure is described in U.S. Pat. No. 5,810,388. The '388 patent describes a method of manufacturing an automotive instrument panel that conceals an airbag door. The steps of manufacturing the instrument panel include providing a molded substrate having first and second surfaces and an aperture therethough, and a metal door having a generally U-shaped slot secured to the second surface of the substrate with a plurality of attaching posts. The slot has first and second ends being spaced apart a distance greater than the length of the aperture. The slot defines a flap in the door. The flap has a width greater than the width of the aperture. The door and substrate assembly is placed within a mold tool and a pre-molded covering is juxtaposed the substrate. A quantity of foam is injected between the substrate and covering and secures the covering to the substrate.
Recently, certain automobile manufactures have implemented airbag door test criteria limiting the amount of fragmentation upon deployment. Fragmentation generally refers to those portions of the airbag door, instrument panel or their surrounding structures which may become separated from their respective components upon airbag deployment and subsequently enter into the vehicle occupant compartment, possibly at the risk of injury to a vehicle occupant. More specifically, some automobile manufactures have sought to limit the possibility of foam fragmentation occurring upon airbag deployment. The '388 patent does not provide a structure for reduced levels of foam fragmentation or a method for such.
In addition, it has become desirable to develop airbag doors with increased stiffness in order to reduce airbag door bending and distortion during deployment and, more particularly, the associated deployment force and energy losses occuring with such bending and distortion. Such increases in airbag door stiffness result in increased transmission efficiency of airbag deployment forces in separating the airbag door from its trim member, in this case an instrument panel. More particularly, airbag doors with increased stiffness tend to deploy in a more uniform and efficient manner given better transmission of deployment forces in a more even array. While the '388 patent provides for some increased stiffness of the airbag door by virtue of indentations of the metal door, it has been found that additional stiffness and resistance to bending is preferred in certain instances. This has been particularly evident with the use of so called “second generation”, “depowered” or “dual stage” airbag systems. Such systems are designed to emit lower energy levels and associated deployment forces upon the detection of an out-of-position vehicle occupant than the previous first generation systems. In such an instance, it has been found that airbag doors with increased stiffness and transmission efficiency of deployment forces are desired for better operation of the airbag system and, more particularly, separation of the airbag door from its trim member with reduced fragmentation.
In addition, it has become desirable to develop trim member substrates and, in particular, instrument panel substrates with a reduced possibility of fragmentation occuring, but still using the same low cost materials. It has been found that fragmentation from the instrument panel substrate is more apt to occur closer to the airbag door area than from other areas of the instrument panel. The '388 patent does not provide a structure for reduced levels of such substrate fragmentation or a method for such.